Double wall heat exchanger utilizing flexible conductor plates between the walls



p 1969 KESTEMONT 3, 3

DOUBLE WALL HEAT EXCHANGER UTILIZING FLEXIBLE CONDUCTOR PLATES BETWEENTHE WALLS Filed Aug. 25, 1966 Sheet 1 of 2 INVENTOR LUCIEN KESTEHONTATTORNEYS April 15, 1969 L. KESTEMONT 3,438,430

DOUBLE WALL HEAT EXCHANGER UTILIZING FLEXIBLE CONDUCTOR PLATES BETWEENTHE WALLS Filed Aug. 25, 1966 Sheet 2 of 2 ATTORNEYS United StatesPatent 17,548 Int. Cl. G05d 23/08; F28f 27/02, 13/08 U.S. Cl. 16532 2Claims ABSTRACT OF THE DISCLOSURE A heat exchanger having two spacedwalls with gas therebetween and a bimetallic flexible conductor plateengaging the walls with a force which is variable in response totemperature changes.

This invention relates to a double-walled heat-exchanger. Suchexchangers prevent the consequences of leaks or breaks in a wall. In thenuclear industry, for example for the production of irradiation capsulesfor the NaK-water exchangers of rapid reactors, or for some fuelelements of nuclear reactors, it is in practice in many cases essential,from the safety point of view, to place double walls between the mediathat have to exchange calories, without permitting the slightest contactor the slightest pollution of one medium by the other. This doublesealing-tightness, which is necessary among other things for theprovision of leak-detecting systems in the space between the walls so asto detect the beginning of a break in good time, inevitably results inpronounced temperature drops when this inter-wall space is full of gas.

The problem might be solved or reduced by filling this space with aliquid, for example a liquid metal that conducts heat well. But if thismethod is adopted, there is a risk of incompatibility or reactionbetween the liquid metal and other materials forming, for example,

' hot medium (the fuel element, the sample to be irradiated or thecalorie-carrying fluid), or between the liquid metal and the coolingcarlorie-carrying fluid. Another disadvantage of this solution is thatwith small leakages there may be solubility in this liquid, and thisprevents detection.

Another possible solution would be to use extremely thick single walls,or even to separate the hot and cold media altogether while leaving asolid connection between them. The thermal efficiency of this system islow.

Alternatively, a gas-filled space might be provided between the walls,the hot and cold structures being made continuous at certain points orin certain portions. But owing to the heat gradients between the twozones in question, any rigid connection produces mechanical stresses,which may make the system impracticable.

The invention employs another solution with a gas space. Instead of arigid connection, it proposes a flexible connection permitting a certainamount of play and differential expansion between the two zones.

In a double-walled heat-exchanger according to this invention, flexibleplates made of a material that is a good conductor of heat are disposedin the space between the two walls and engage with these two walls, soas to produce by contact, good conduction of heat between the latter,the space between the two walls is filled with a gas, there is at leastone detector for contamination of the gas by leakage through a wall ofthe container and means for circulating the gas so that it passes(preferably slowly) through the leak detectors.

Some specific embodiments of the invention will now be 3,438,430Patented Apr. 15, 1969 described by way of example with reference to theaccompanying drawings in which:

FIGURE 1 is a cross-section of part of a heat-exchanger according to theinvention,

FIGURES 2, 3 and 4 are cross-sections of heat-exchangers according tothe invention, and

FIGURES 5 and 6 are cross-sections of parts of heatexchangers accordingto the invention, wherein the flexible plates are made of bimetallicmaterial.

These figures only show the elements necessary for an understanding ofthe invention; the corresponding elements of these figures haveidentical reference numbers.

FIGURE 1 shows part of a heat-exchanger between a hot medium 1 and acolder medium 2, comprising two walls, the hot wall 3 and the cold wall4, with a gas-filled inter-wall space 5 between them. So that anyleakages in either of the walls 3 or 4 may be detected as soon aspossible, the gas travels through a circuit (not shown), which causes itto pass through leak-detectors (also not shown). These leak-detectorsmay be inside or outside the space 5. The same applies to the means forsetting the gas in motion.

Heat transmission between the walls 3 and 4 is effected across the space5 by means of resiliently fiexible plates, for example 6, made of amaterial that is a good conductor of heat and does not absorb neutronsto any great extent, if a neutron medium is present (for exampleirradiation capsules or fuel elements). These plates are simply engagedagainst both walls 3 and 4, the force with which they engage these wallsand consequently their heat-conducting properties depending essentiallyon their outline, thickness and elasticity. In view of their elasticityand the fact that they are not welded or attached to the walls, anydifferential deformations of these walls can be effected freely withoutcausing mechanical stresses, as the plates can be deformed and slide onthe walls. All that is necessary is to provide sufiicient space betweentwo adjacent plates. To prevent these plates from moving from oneposition to another position nearby, it is preferable, although notessential, to form in at least one of the two walls longitudinalgrooves, for example 7, in which corners or projections of the outlineof the flexible plates 6 can be wedged. To make drawing easier, theplates are shown in all the figures except the last one as havingV-shaped cross-sections, but other forms and other cross-sections, forexample triangular, circular, trapezoidal, X-shaped or M-shaped, aresuitable.

FIGURES 5 and 6 show heat-exchangers according to the invention in whichthe flexible conductive plates 6 are bimetallic, so that these platestend to straighten as a result of an increase in temperature. When thetemperature of the hot wall, for example, increases, the plates 6 beginto straighten and bear harder on the walls 3 and 4, thereby improvingthe heat conduction at the plate-wall contact surfaces. As a result, theheat-transfer properties of the exchanger are automatically controlledaccording to the temperature. With bimetallic plates also, of course,many shapes or cross-sections are suitable, and can be so chosen thatthe plates react to a temperature increase by bearing harder on thewalls.

I claim:

1. A heat exchanger comprising an outer wall, an inner wall disposedwithin said outer wall and spaced therefrom, means for circulating a gasthrough the space between said walls, means to detect leakage of gasthrough said walls, and at least one bimetallic flexible conductor platedisposed in said space and engaging said walls with a predeterminedforce, said plate being adapted to vary said force in response totemperature changes.

2. The heat exchanger of claim 1, wherein at least one groove is formedin at least one of said walls and is adapted to receive a correspondingend of said plate to walls 3 4 prevent said plate from moving withrespect to said 3,106,526 10/1963 Wolfe et a1 176-87 X 3,216,902 11/1965Costes et a1 176-87 X References Cited FOREIGN PATENTS UNITED STATESPATENTS r 835,297 5/1960 Great Britain. Evans X o Glfiat Bl'ltall'l.5/1955 Bonvillian et a1. 138148 X ROBERT A *LEARY P E 8/1960 Smith165-32 0 Timmy f 1/1962 Lovingham 165 154 X ALBERT W. DAVIS, AsszstantExammer. 1/1963 Young 176-52 10 7/1963 Schluderberg 165-11 X 9/1963Speidel et a1 176-58 X 165-154, 81, 185; 220-9; 176-87, 52; 138-113

